The behaviour question: how can I lessen the impact of low-level disruption?

Low-level disruptions are small and subtle acts of misbehaviour, which often are deliberate and aimed at irritating the teacher in order to distract him/her and the class from the lesson and get some amusement instead. It includes things like: rocking on a chair, pen-tapping, chatting over others, chatting over the teacher, passing notes, giggling, entering [...]